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As officials released frantic 911 calls placed after the deadly Northern California bus crash, fellow students paid tribute to those killed at the site of the fatal wreck. Patrick Healy reports for the NBC4 News at 11 p.m. Thursday, April 17, 2014. (Published Friday, April 18, 2014)

The 911 calls released Thursday reveal audible cries of fear in the moments after the fiery Northern California bus crash that claimed 10 lives while en route to Humboldt State University last Thursday.

California Highway Patrol Capt. Todd Morrison said that investigators will conduct vehicle tests using a 2014 tour bus and a 2007 FedEx tractor-trailer truck to learn more about characteristics such as braking and visibility.

“We are hoping to learn how it happened so that we can identify what to do to prevent it from happening again,” Morrison said.

Investigators were also still interviewing passengers, witnesses and urging anyone with video of the crash to send it to authorities. They also attempted to recreate the crash scene with similar vehicles to try to gain insight.

"We owe it to the families of the involved families and the victims of this tragic collision that we tell the story of what happened, and that we tell it as accurately as possible," Leal said.

All 10 victims in the crash had been identified, some by authorities and others by family, including a recently engaged couple, a college admissions counselor and the the drivers of the truck and bus.

Fellow students returned to the scene of the crash Thursday to pay tribute to those killed one week ago.

Glenn County Sheriff-Coroner Larry Jones said most of the victims had been positively identified by his office, but their causes of death were being withhel pending toxicology testing.

"That can be several weeks out before we receieve all of that data from the labatory," Jones said.